AUTHOR=Asaeda Takashi , Rashid Md Harun , Schoelynck Jonas 

TITLE=Tissue Hydrogen Peroxide Concentration Can Explain the Invasiveness of Aquatic Macrophytes: A Modeling Perspective

JOURNAL=Frontiers in Environmental Science

VOLUME=8

YEAR=2021

URL=https://www.frontiersin.org/journals/environmental-science/articles/10.3389/fenvs.2020.516301

DOI=10.3389/fenvs.2020.516301

ISSN=2296-665X

ABSTRACT=<p>In recent years, an invasive macrophyte, <italic>Egeria densa</italic>, has overwhelmingly colonized some midstream reaches of Japanese rivers. This study was designed to determine how <italic>E. densa</italic> has been able to colonize these areas and to assess the environmental conditions that limit or even prevent colonization. Invasive species (<italic>E. densa</italic> and <italic>Elodea nuttallii</italic>), and Japanese native species (<italic>Myriophyllum spicatum</italic>, <italic>Ceratophyllum demersum</italic>, and <italic>Potamogeton crispuss</italic>) were kept in experimental tanks and a flume with different environmental conditions. Tissue hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) concentrations were measured responding to either individual or multiple environmental factors of light intensity, water temperature, and water flow velocity. In addition, plants were sampled in rivers across Japan, and environmental conditions were measured. The H<sub>2</sub>O<sub>2</sub> concentration increased in parallel to the increment of unpreferable levels of each abiotic factor, and the trend was independent of other factors. The total H<sub>2</sub>O<sub>2</sub> concentration is provided by the sum of contribution of each factor. Under increased total H<sub>2</sub>O<sub>2</sub> concentration, plants first started to decrease in chlorophyll concentration, then reduce their growth rate, and subsequently reduce their biomass. The H<sub>2</sub>O<sub>2</sub> concentration threshold, beyond which degradation is initiated, was between 15 and 20 µmol/gFW regardless of the environmental factors. These results highlight the potential efficacy of total H<sub>2</sub>O<sub>2</sub> concentration as a proxy for the overall environmental condition. In Japanese rivers, major environmental factors limiting macrophyte colonization were identified as water temperature, high solar radiation, and flow velocity. The relationship between the unpreferable levels of these factors and H<sub>2</sub>O<sub>2</sub> concentration was empirically obtained for these species. Then a mathematical model was developed to predict the colonization area of these species with environmental conditions. The tissue H<sub>2</sub>O<sub>2</sub> concentration decreases with increasing temperature for <italic>E. densa</italic> and increases for other species, including native species. Therefore, native species grow intensively in spring; however, they often deteriorate in summer. For <italic>E. densa</italic>, on the other hand, H<sub>2</sub>O<sub>2</sub> concentration decreases with high water temperature in summer, allowing intensive growth. High solar radiation increases the H<sub>2</sub>O<sub>2</sub> concentration, deteriorating the plant. Although the H<sub>2</sub>O<sub>2</sub> concentration of <italic>E. densa</italic> increases with low water temperature in winter, it can survive in deep water with low H<sub>2</sub>O<sub>2</sub> concentration due to diffused solar radiation. Currently, river rehabilitation has created a deep zone in the channel, which supports the growth and spreading of <italic>E. densa</italic>.</p>